The present invention relates generally to apparatus for automatically shutting off unwanted fluid flow in pipes, and more specifically to a novel combination piezoelectric film transducer and signal conditioning circuitry.
Damage to buildings and equipment from water pipes cracking or breaking during unattended periods such as evenings and weekends is a well-known problem. The problem is made worse in the case of pipes carrying chemicals such as flammable and corrosives. The damage can be avoided or greatly reduced if immediate corrective action is taken to stop the fluid flow.
Prior art appratus to solve this problem generally use leakage detectors to automatically trigger flow shutoff valves. Prior art leakage detectors generally work either by detecting the presence of fluid outside the pipe, or by detecting the presence of a flow, or an unusual flow rate, at a distance from the damaged area of pipe.
Prior art detectors that detect the presence of fluid outside a pipe generally do not provide a trigger signal sufficient to activate a flow shutoff valve until after a substantial amount of fluid has leaked and damage already occurred.
Prior art detectors which detect abnormal flow rates at locations away from the pipe sections where leakage may occur are generally elaborate flow measuring devices placed inside the pipes. Their complexity prevents distributing reasonable numbers of such devices over a large facility and makes their use as a retrofit in an existing facility extremely difficult. An improvement is piezoelectric crystal transducers which can be placed on the outside of pipes to detect vibrations resulting from the flow of fluid within the pipe. These piezoelectric crystal transducers respond generally to ultrasonic frequencies and require accompanying circuitry to amplify, condition and distinguish their electrical output to identify when appropriate vibration is present and to trigger shutoff valves. The circuitry is in many cases overly complex and subject to both failure to detect leaks and to false alarms.
It is, therefore, a principal object of the present invention to provide an improved flow detector using a piezoelectric transducer and simple circuitry that provide an accurate trigger signal identifying unwanted fluid flow in a pipe and which will activate a shutoff valve.
It is another object of the present invention to provide piezoelectric transducer circuitry that is easily tuned for different conditions and pipes.
It is yet another object of the present invention to provide piezoelectric transducer circuitry that avoids false and spurious signals.
A feature of the present invention is that it is non-invasive and may be easily retro-fitted to existing installations.